The present invention relates to the removal of organic sulfur compounds such as carbonoxysulfide (COS), carbon sulfide (CS.sub.2), and mercaptans, possibly in addition to hydrogen sulfide, from gasses herein called host gases which contain these compounds, and using scrubbing of the host gas at normal or elevated pressure and at temperatures in the range between 20 and 200 degrees centigrade under utilization of a particular scrubbing solution. The invention relates particularly to such a solution. The method is to be applicable to any kind of gasses which may contain these compounds as contaminants. Examples for host gasses are, for example, natural gas, coke gas, water gas, generator gas, and gasses originating in carbon gasification equipment but also to all kinds of exhaust fumes that may contain any of these compounds.
From a somewhat different point of view, the invention relates to a method for the removal of sulfur oxides (SOX) and/or nitrogen oxides (NOX) from host gasses under utilization of reducing compounds using also scrubbing of the host gas at a normal or elevated pressure at a temperature between 20 and 200 degree centigrade, using for scrubbing also a solution. Examples for the host gas which may contain SOX and/or NOX are smog, smoke, fume, exhaust gasses, resulting, for example, from sulfuric acid nitrogen acid production, roasting gasses or the like.
Generally speaking, it is known to remove organically bound sulfur from a host gas under utilization of an alkali medium such as a watery solution of carbonates, bicarbonates, borate, phosphate, of alkali metal, or under utilization of solutions containing organic alkyl amines, aryl amines, and alkanolamines. Any CO.sub.2 contained in the host gas is also absorbed, but that amounts to an additional and unnecessary expenditure.
The removal of carbon-oxy-sulfide COS and CS2 by means of the presently used scrubbing process, particularly for removal of the acidic contaminants H2S and CO2, is insufficient. A variety of proposals have been made to solve this problem to be briefly described as follows. Among the known methods for the removal of organically bound sulfur, the most successful procedure involves the heterogenic, catalytic conversion of the contaminant into hydrogen sulfide. As a catalyst, one uses here heavy metals such as iron, lead, molybdenum, nickel, tungsten, and preferably the sulfides of these metals. Also, CO converting catalysts, direct or in modified form, are used. However, all these heterogenic, catalytic methods even when in any variety are disadvantaged by the fact that one has to use high temperatures such as at least 300, up to 600 degrees centigrade.
Therefore, it has been suggested in the alternative to treat gasses at such high temperatures with basic reacting salts of unorganic or organic bases, solved in water or alcohol so that the contaminants, such as COS and CS2, are changed by means of hydrolysis into hydrogen-sulfide which, in turn, can be removed together with the host gas from the reaction zone. The problem here, however, is that the requisite basicity of the scrubbing medium has to be maintained in spite of the presence of H2S and CO2. These compounds are to be converted into sulfides and carbonates or bi-sulfides and bi-carbonates and, therefore, reduce the basicity of the material as a whole. The hydrogen-sulfide that is present as well as it forms catalytically will then have to be removed from the gas in a separate step.
Other methods for removal of sulfur-oxyde and/or nitrogen-oxyde from smog and smoke fumes are known such as a catalytic as well as non-catalytic oxidation of SO2 and NOX under utilization of oxygen, ozone or the like. Herein then takes place a catalytic as well as a non-catalytic reduction of these contaminants under formation of ammonia followed by wet absorption of the acidic contaminants SOX and NOX through a watery solution or a suspension. In case any temperature variation is observed, as well as in case of non-stoichiometric composition of the redox system difficulties will be encountered, such as the emission of one of the reaction participants. Therefore, one has used catalysts as a reaction aid which will operate in an optimum temperature range from 350 to 450 degrees centigrade. Generally speaking the combustion requires pyrotechnical steps to be taken, and will reduce the NOX emission values only to a minimum extent. Also, they require a rather difficult realizable change in the combustion process, which in the case of refurnishing existing equipment, may entail large expenditures.
In Japan redox reactions are already used for removing SO2 and NOX. These methods are disadvantaged by the fact that they use up large quantities of rather valuable products such as hydrogen peroxide is used as an oxidizer, or ammonnia if used as a reduction medium. Moreover, the danger exists in catalytic reduction and in case of reaction vessels being heated by coal that the catalysts maybe rendered ineffective by the dust. On the other hand wet precipitation has the advantage that not only will NOX and SOX be removed but the precipitation of dust and removal is a fortunate side effect.